<h1 id="maine-congressional-districts">2020 Maine Congressional
Districts</h1>
<h2 id="redistricting-requirements">Redistricting requirements</h2>
<p><a
href="https://legislature.maine.gov/legis/statutes/21-A/title21-Asec1206.html">In
Maine, following Title 21-A, Chapter 15, Section 1206, districts
must</a>:</p>
<ol type="1">
<li>be contiguous (1)</li>
<li>have equal populations (1)</li>
<li>be geographically compact (1)</li>
<li>preserve county and municipality boundaries as much as possible
(1)</li>
</ol>
<h3 id="algorithmic-constraints">Algorithmic Constraints</h3>
<p>We enforce a maximum population deviation of 0.5%. We apply the
standard algorithmic county constraint.</p>
<h2 id="data-sources">Data Sources</h2>
<p>Data for Maine comes from the <a
href="https://dataverse.harvard.edu/dataverse/electionscience">Voting
and Election Science Team</a> for 2016, 2018, and 2020. It is
retabulated to 2020 Census tracts, as 2020 Census VTDs do not cover the
majority of Maine’s geography.</p>
<h2 id="pre-processing-notes">Pre-processing Notes</h2>
<p>Islands tracts were connected to the nearest tract within the same
district.</p>
<h2 id="simulation-notes">Simulation Notes</h2>
<p>We sample 5,000 districting plans for Maine across 4 independent runs
of the SMC algorithm. We use the standard county constraint. We weaken
the compactness parameter to 0.9 due to the relatively small state size
and total number of tracts to encourage more diversity in the
sample.</p>
<h2 id="contents">Contents</h2>
<ul>
<li><code>ME_cd_2020_stats.csv</code> contains summary statistics on the
sampled redistricting plans</li>
<li><code>ME_cd_2020_plans.rds</code> is a compressed
<code>redist_plans</code> object, which contains the matrix of
precinct/block assignments and may be used for further analysis.</li>
<li><code>ME_cd_2020_map.rds</code> is a compressed
<code>redist_map</code> object, which contains the precinct/block
shapefile and demographic data.</li>
</ul>
<p>Both the <code>redist_plans</code> and <code>redist_map</code> object
are intended to be used with the <a
href="https://alarm-redist.github.io/redist/">redist package</a>.</p>
<h3 id="codebook-for-summary-statistics">Codebook for summary
statistics</h3>
<ul>
<li><code>draw</code>: unique identifier for each sample. Non-numeric
draw names are real-world plans, e.g., <code>cd_2010</code> for an
enacted 2010 plan.</li>
<li><code>district</code>: a district identifier. District numbers
roughly match those in the enacted plan, but the correspondence is not
perfect.</li>
<li><code>chain</code>: a number identifying the run of the
redistricting algorithm used to produce this draw. Used for diagnostic
purposes.</li>
<li><code>pop_overlap</code>: a number indicating the fraction of people
in this plan who reside in the same-numbered district in the enacted
plan.</li>
<li><code>total_pop</code>: the total population of each district.</li>
<li><code>total_vap</code>: the total voting-aged population of each
district.</li>
<li><code>pop_*</code>, <code>vap_*</code>: total (voting-aged)
population within racial and ethnic groups for each district. Variable
codes documented <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>plan_dev</code>: the maximum population deviation among
districts in the plan. Computed as
<code>max(abs(distr_pop - target_pop)/target_pop)</code>.</li>
<li><code>comp_edge</code>: compactness, as measured by the fraction of
internal edges kept. Higher values indicate more compactness.</li>
<li><code>comp_polsby</code>: compactness, as measured by the
Polsby-Popper score. Higher values indicate more compactness.</li>
<li><code>county_splits</code>: the number of counties which belong to
more than one district.</li>
<li><code>muni_splits</code>: the number of Census Designated Places
which belong to more than one district.</li>
<li><code>*_##_dem_*</code>, <code>*_##_rep_*</code>: vote counts for
statewide Democratic and Republican candidates in a certain election.
More information <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>adv_##</code>, <code>arv_##</code>: average vote counts for
statewide Democratic and Republican candidates in a certain year. More
information <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>ndv</code>, <code>nrv</code>: averages of the
<code>adv_##</code> and <code>arv_##</code> variables across all
available elections.</li>
<li><code>ndshare</code>: normal Democratic share, computed as
<code>ndv / (ndv + nrv)</code></li>
<li><code>e_dvs</code>: average Democratic vote share, computed as the
average of the Democratic vote share when first scored under each
statewide election.</li>
<li><code>pr_dem</code>: probability seat is represented by a Democrat;
calculated as the fraction of statewide elections under which the
district had a majority Democratic share.</li>
<li><code>e_dem</code>: expected number of Democratic seats for the
plan; equivalent to summing the <code>pr_dem</code> values across
districts</li>
<li><code>pbias</code>: partisan bias at 50% vote share, averaged across
all available elections. Positive values indicate Republican bias.</li>
<li><code>egap</code>: the efficiency gap, averaged across all available
elections. Positive values indicate Republican bias.</li>
</ul>
